Method for surface testing
US4681442A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Mar 18, 1985 |
| Grant date | Jul 21, 1987 |
| Priority date | — |
| Expiry date | Mar 18, 2005 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG02B21/10
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
This teaches a method and device for testing of the surface of a transparent object such as a photolithographic mask in which respective recordings with darkfield reflection illumination and darkfield transmission illumination is made, and the intensities measured are compared to form a different image, in which defects are characterized by high local levels of light intensity. Both recordings can be generated in a point-by-point mode if the surface is scanned by a focussed laser beam. In another embodiment, two recordings of the entire surface are digitized, and examined arithmetically for local image differences. Surfaces of opaque bodies can also be examined with the difference image of two darkfield reflection recordings made at different angles of illumination.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.